This invention relates to polyphenylene ether compositions and more particularly to impact-modified polyphenylene ether compositions having improved processability, and to a method for improving the processability of impact-modified polyphenylene ether compositions.
Polyphenylene ether (PPE) resins have long been known as high temperature thermoplastics. For example, PPO, or poly(2,6-dimethyl-1,4-phenylene ether) was disclosed and described in U.S. Pat. Nos. 3,134,753 and 3,306,874. More recently, in U.S. Pat. No. 4,011,200 phenylene ether copolymer resins having improved thermal stability were described. PPE resins generally soften or melt only at very high temperatures and are very difficult to melt process in conventional molding equipment. Commonly, PPE resins are blended with lower melt temperature resins to improve their melt processability and to achieve commercially acceptable molding characteristics. For example, blends of polyphenylene ether resins with styrenic resins such as those shown in U.S. Pat. Nos. 3,356,761, 3,383,435 and 4,038,543 are considerably more readily processable than PPE resins alone, and have found substantial commercial application as molding resins. Although blends of polyphenylene ether resins with lower melt temperature styrenic resins may be formulated to have good mechanical properties and are much improved in processability over the polyphenylene ether resins alone, such blends generally exhibit a significantly lowered heat distortion temperature compared with that of the corresponding PPE resin. Consequently, the upper use temperature limits for these blends is reduced below that of polyphenylene ether resins alone.
Blends of poly(2,6-disubstituted)phenylene ether resins, and particularly PPO, with a variety of rubbery impact modifiers have also been disclosed in the art. For example, high impact blends of PPO containing greater than 30 wt% of a combination of block copolymer rubbers were disclosed in U.S. Pat. No. 4,113,800. In U.S. Pat. No. 4,167,507 there are disclosed impact modified blends of PPO and a hydrogenated ABA block copolymer rubber. These latter blends include a plasticizer and a styrenic resin to achieve processability, which in turn substantially depress the HDT value of these resin blends. In U.S. Pat. No. 3,660,531, rubber modified blends of PPO are shown to have greatly enhanced processability when a styrenic resin is included. Again, the including of a styrenic resin and/or a plasticizer substantially reduces the HDT value for such blends and limits their upper end-use temperature properties.
The market place continues to find a need for processable high impact thermoplastic resins with a good balance of mechanical properties and even higher end-use temperature performance, demands which are not satisfactorily met by the presently available resin compositions.